What happens to a DC fan if the positive and negative poles are connected backwards?

If the DC fan uses a permanent magnet motor with commutator, the motor reverses after the power supply is reversed. If the dc motor with stator coil is used (the motor with excitation), the steering remains unchanged, and the steering can be changed only by changing the direction of excitation or rotor current. If the DC fan is now such as the computer CPU fan structure, with electronic converter fan, after the power supply is reversed, the internal circuit can not work properly, so it will not rotate, the circuit may be damaged.